- -,:'- • ... , \ This paper not to be ci ted without prior reference to the author International Cauncil for CM 198J/G:18 the Exploration of the Sea Demersal Fish Committee • PRELIMINARY STUDIES OF THE EXPLOITED STOCK OF KITEFIN SHARK Scymnorhinus licha (BONNATERRE, 1788) IN THE AZORES. by Helder Marques da Silva Universidade dos A90res Departamento de Oceanografia e Pescas 9900 HORTA - AQORES - PORTUGAL ABSTRACT Information is given about the commercial fishery for the Kitefin shark Scymnorhinus licha (Bonnaterre, 1788) in the Azores. Efforts to determine age, and some observations on the reproduction, embryology and food habits are discussed. A length/weight relationship is established for each sex sepa rately. Catch and effort data (1977 - 1982 period) are analy- sed and Maximum Sustainable Yield (MSY) calculated for the fi shery around the islands Faial and Pico. On definit l'interet commercial du "lixa", Scymnorhinus licha-(Bonnaterre, 1788), aux Azores. L'age ne fut pas encore determine avec riguer, la -situation des recherehes sur ce point est presente." On fournit quelques observations sur la reproduction, l'embriologie et les habitudes alimentaires. La relation taille/poids du corps est etabli pour chaque sexe. Des analyses sur les donnes de prise et effort sont faites pour le periode 1977 - 1982 et la Capture Maximale ble (MSY) est determinee pour les lIes Faial et Pico.
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- -,:'-•..., \
This paper not to be ci ted without prior reference to the author
International Cauncil for CM 198J/G:18
the Exploration of the Sea Demersal Fish Committee
•
PRELIMINARY STUDIES OF THE EXPLOITED STOCK OF KITEFIN SHARK
Scymnorhinus licha (BONNATERRE, 1788) IN THE AZORES.
by
Helder Marques da Silva
Universidade dos A90res
Departamento de Oceanografia e Pescas
9900 HORTA - AQORES - PORTUGAL
ABSTRACT
Information is given about the commercial fishery for
the Kitefin shark Scymnorhinus licha (Bonnaterre, 1788) in
the Azores. Efforts to determine age, and some observations
on the reproduction, embryology and food habits are discussed.
A length/weight relationship is established for each sex sepa
rately. Catch and effort data (1977 - 1982 period) are analy
sed and Maximum Sustainable Yield (MSY) calculated for the fi
shery around the islands Faial and Pico.
RES~
On definit l'interet commercial du "lixa", Scymnorhinus
licha-(Bonnaterre, 1788), aux Azores. L'age ne fut pas encore
determine avec riguer, la -situation des recherehes sur ce
point est presente." On fournit quelques observations sur la
reproduction, l'embriologie et les habitudes alimentaires. La
relation taille/poids du corps est etabli pour chaque sexe.
Des analyses sur les donnes de prise et effort sont faites
pour le periode 1977 - 1982 et la Capture Maximale Sustenta~
ble (MSY) est determinee pour les lIes Faial et Pico.
funk-haas
Neuer Stempel
..
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INTRODUCTION
The Kitefin shark is cosmopolitan in distribution, oc
curing mainly in warmer seas. It is found regularly from the
Irish Atlantic slope to off Marocco, Madeira and Azores. It
is also present in the western Atlantic, South African waters,
and around New Zealand and Australia, Japan and Taiwan. It is
a benthic, sometimes mesopelagic, species, which lives in
depths ranging from 90 to about 1000 m, mainly on slope areas
between )00 and 700 m. In Azores, its mainly caught at 150
-200 m, the deepermost record from 500 m (KREFFT & TORTONESE,
1973) •
Besides the Blackspot seabream (Pagellus bogaraveo),
the Kitefin shark represents the most important demersal spe
eies in the Azores. In 1981 the recorded catch w-as 2.239 thou
sand tonnes, making 19 percent of the total fish catch in the
Azores. However, it is fished only around three of the islands:
Pico, Faial, and San Niguel. In Pico it is the most important
species in the fishery.
Traditionally, the fishery for Kitefin shark has been
an artisanal fishery from small boats using vertical handlines.
In later years this fishery has also been taken up by larger
'boats using nets.
The flesh of the Kitefin shark is dried and exported
to continental Portugal where it is much appreciated. Its li
ver, which represents approximately 20 percent of the total
body weight, yields a thin.oil with a high content of squalen,
and is exported.
The biology of the Kitefin shark is poorly known, but
beeing a viviparous with a long period of gestation and rela~
tively few offspring, it will be sensitive to exploitation.
MATERIAL AND NETHODS
It has been possible to obtain 21 specimens for com
plete biological samples, from Azorean research vessel R/V
"Geralda" , from the Portuguese research vessel R/V "r;oruega",
., \
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and from loeal fishermen. All speeimens were taken from Se
ptember 1982 to July 1983, and the sites o~ eapture are given
in Figure 1. In addition, 274 speeimens has been measured and
weighed at the factory "Maria Gon9alves" in Pico.
For all" fish the sex was recorded, the total length
measured to the nearest em below, and the weight to nearest
50 g.
For eomplete biologieal sampIes the previous data were
reeorded, as weIl as length of elasper in males (TESHI}~ et
al, 1971), number of embryos, number of eggs, length of embrz
os and diameter of eggs ~or ~emales, and also the weight o~
gonads in both sexes and the weight of the liver. Par stomach
content studies the ~ull and empty stomach weight as weIl as
the liquid and solid content weight were measured. The solid
contents were than put in unbleached cloth bags and the bags
introduced in 10% formalin. For age determination vertebral
sections were prepared aceording to DAIBER (1960).
Basic information about catch and number of crew for
each vessel for the islands Pico and Faial for 1977 - 1982
has been obtained from the "Servigo Agoriano de Lotas" and
compiled by staff from the "Departamento de Oceanografia e
Peseas". Although such information exists also for the years
1972 - 1976, it is judged to be unreliable (SILVA, 1982).
From San Miguel information about the number o~ crew is not
available.
It is assumed that for the artisanal fishery with hand
lines the number of lines,.and hence the effort, is proporti~
nal to the number of crew. For the"modern" fishery with nets
the number,of nets used by each boat is not known. It seems,
however, that the number of nets is not closely dependent on
the number of crew, and a reliable measure for effort is
therefore only available for the artisanal fishery." For these
reasons it has been decided to use effort data only from the
artisanal fishery, with "man trip" as the unit of effort.
With the above data, the ~itting o~ a Graham curve (according
to RICKER, 1975) to the fishery around Pico and Paial has
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been attempted, using the data given in Table 3.
RESULTS AND DISCUSSION
1. Age determination
Daiber's technique for age determination (DAIBER, 1960)
in the Skate Raja eglanteria has been attempted for Scymnorhi
~ licha. This technique inc1udes dehydration with 10 per
cent formalin and absolute alcoho1, than paraffin impregna
tion and finally xylene clearing. After preparation according
to this author's method vertebrae were observed with different
amplifications but no rings could be distinguished. Also thin
cuts, from 0.3 mm to 1 mrn have been observed with a HITUTOYO
profile projector (transrnitted light) without any positive re
sults.
However,opaque rings alternating with gray trans lu
cent rings became visible to the naked eye, using a good re
flected light. These rings were not all equally distinct in
all vertebrae of the same vertebral column. Not only the dis
tinctness of the ring varied, but also the number of visible
rings. In one female specimen of 140 cm and 16.15 Kg, 9 to 13
rings could be counted betweenthe 21st
and the 30th verte-th
brae. Posterior to the JO vertebra the number of visible
rings decreased progressvely and after the 57 thno rings were
distinguishable. Anterior to the 21st
vertebra, the number of
clearly visible rings also decreased, and rings could not be
distinguished in the four most anterior vertebrae.
Immersion of vertebrae and vertebral sections in mure -
xid before observation with different amplifications did not
giye results either.
2. Lengthjweight relationship
Lengthjweight relationship have been calculated separa
tely for males and females according to the formula:
bW = a.L
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where W is weight in Kg, L is length in cm, and a and bare
the parameters to be determined. Using logarithmic transform~
tions of lengths and weights for each individual and regres
sion analysis, the following formulas were obtained: